Essential tremor (ET) is the most common movement disorder in the United States and currently affects an estimated 10 million individuals. Its prevalence increases with age, making it a growing concern for the U.S. aging population. ET affects 6.3% of the population over 65, but over 20% of people over the age of 95. It is characterized by 4-7 Hz oscillatory movement in the distal limbs, especially the hands. Unlike Parkinsonian tremor, which predominantly occurs during rest, essential tremor is postural (induced by holding a limb against gravity) and kinetic (present during movement).
Tremor is also a significant problem for patients with orthostatic tremor, multiple sclerosis, dystonia and Parkinson's disease. Although the underlying etiology of tremor in these conditions differs from that of ET, treatment options are similarly limited.
A number of conditions, such as tremors, can be treated through some form of transcutaneous peripheral nerve stimulation. Previous work and patent applications (e.g., PCT/US2014/012388, PCT/US2015/033809, PCT/US2016/037080) have focused on applying stimulation to the median, radial, and/or ulnar nerves on the arm or wrist. However, applying stimulation to the arm or wrist remains challenging because of natural variation in wrist diameter, nerve locations, nerve depolarization characteristics, and skin conduction. This leads to significant challenges in designing a device to comfortably, safely, and reliably stimulate the peripheral nerves across a broad population of potential users. For example, variation in the size and location of the ulnar styloid process (i.e., a bony formation on the wrist) may prevent the comfortable application of a wrist-worn stimulator that requires an electrode to conform to the wearer's skin. Additionally, as the wrist has a large range of motion with many tendons, there may be greater variability in stimulation sensation of a wrist worn stimulator due to normal hand motion.